Four of six patients with gyrate atrophy of the choroid and retina, with hyperornithinemia, and ornithine keto-acid amino transferase deficiency have been found to show in vitro responsiveness of cultured fibroblasts to increasing concentrations of pyridoxal phosphate. Five of the six have been evaluated for clinical responsiveness (lowering of elevated serum ornithine) and three appear to respond in vivo. Two of the three in vivo B6 responders have shown improvement of electroretinography when treated and decreased electroretinographic responses when supplemented B6 was discontinued. Mild improvement of electrooculography was seen but the significance is uncertain. A total of 19 members of six families have been studied for common genetic polymorphisms. Further studies on enzyme measurement and the mechanism of this response are in progress.